vous savez que a² - b² = (a+b) (a-b)
donc
C = (2x+1)² - 7² = (2x+1+7) (2x+1-7) = (2x+8) (2x-6) = 2(x+4)*2(x-3) = 4 (x+4) (x-3)
et
C = 0
donc 4 (x+4) (x-3) = 0
soit x + 4 = 0 => x = -4
soit x - 3 = 0 => x = 3
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vous savez que a² - b² = (a+b) (a-b)
donc
C = (2x+1)² - 7² = (2x+1+7) (2x+1-7) = (2x+8) (2x-6) = 2(x+4)*2(x-3) = 4 (x+4) (x-3)
et
C = 0
donc 4 (x+4) (x-3) = 0
soit x + 4 = 0 => x = -4
soit x - 3 = 0 => x = 3